This invention relates to pulse combustion burners, and to gas-fired pulse combustion heating appliances including space heaters incorporating such burners.
The development of suitable pulse combustion furnaces has enabled the advantages and efficiencies of pulse combustion to be attained in residential central heating. In addition to the advantages of self-sustaining operation, the steady state thermal efficiency of such central heating systems may be in the range of 90 to 99% and provide significant operating cost savings. There is a need for a pulse combustion fired space heater to provide comparable advantages and thermal efficiencies.
The development of a suitable space heater involves restrictive size and noise suppression requirements since space heaters are not typically isolated in a basement or closet as in the case of a central heating furnace. For a heater capacity of about 20,000 BTU/hr. to be used in residential applications, the compact size requirements of commercially sized space heaters require that the overall size of the appliance be about 3' long, 2' tall and 1' wide. The sound level of the unit at a distance of 3' should be about 53 dBA or less.
The imposition of size requirements, especially the relatively compact dimensions contemplated herein, are particularly difficult to meet in pulse combustion systems since the resonant operation thereof requires certain geometric configurations and/or size relationships to be observed. More particularly, in pulse combustion burners of the Helmholtz type, an oscillating or pulsed flow of combustion gases through the burner is maintained at a frequency determined by burner component geometry and fuel supply characteristics including mixing the air and fuel components to provide a homogeneous air/fuel mixture. Typically, a combustion chamber of a given size cooperates with a tailpipe or exhaust pipe of specific dimensions to provide explosive combustion cycles, thermal expansion of the combustion gases, and oscillating gas pressures which provide a pulsed flow of combustion gases through the burner with alternating negative and positive pressure phases. In order to make the pulse combustion process self-sustaining, the oscillating gas pressures may be used to provide self-feeding of a combustible gaseous mixture. Accordingly, the close relationship between pulse combustion operation and heater geometry restricts variation in the spatial arrangement and compaction of the heater elements to meet commercial size and sound attenuation requirements. Also, the amounts of circulating air flow necessary for temperature conditioning the spaces must be maintained and adequate heat transfer surfaces must be provided for efficient heat transfer.